A standard type of prosthetic hip-joint socket has an outer support part that is anchored in an appropriately formed recess in the hip joint, and an inner part or insert that fits into this support part and that itself forms the new acetabulum. This two-part construction makes it possible to use a standard-size outer part, and to have a whole set of inserts formed with differently sized acetabulum-forming recesses to accommodate different shaft balls.
French patent document No. 2,099,259 describes such an outer part which has a pin-shaped extension formed with a screwthread. The pelvis must be specially bored out to receive this element and its extension, with considerable destruction of bony tissue. The cavity that is cut in the pelvis for this outer part must be exactly positioned, as the support fits complementarily in it in only one orientation.
Another system is seen in German patent document No. 2,411,617 into which the insert can be snapped. The outer surface of the support is tapered and formed with a screwthread. As in the above-described system, such an arrangement requires that a particularly shaped cavity be formed, and then threaded. The outer support part can only sit in one orientation, normally relative to a central axis or the cavity, in the outer part, so once again this cavity must be formed with enormous care. No adjustment of the orientation of the artificial acetabulum is possible once the cavity for the outer part has been formed in the hip bone.